The perception of three dimensional images is a visual effect created by stereoscopy, visual accommodation, perspective (apparent size dependent on distance), occlusion (objects in front hide what is behind), atmospheric effects (objects in the distance appear hazy), shading, and so on. Images presented by planar displays, such as CRTs, LCDs, projection displays, laser scan displays, and others, provide visual clues of a three dimensional image using perspective, occlusion, shading, and atmospheric effects at a fixed visual focal length that determined by the distance between the display screen and the audience. Stereoscopic displays, such as 3-dimensional LCDs and 3-dimensional head mounted displays, provide spatially distinct images to each eye so that the stereoscopy is also included in the visual clues for the perception of three dimensional images.
Although some 3-dimensional head mounted displays are superior to 3-dimensional LCDs in providing better stereoscopy images, the displayed images are still at a fixed visual focal length while the stereoscopy and visual accommodation are inherently related in the perception of a three dimensional image. Furthermore, because high power lenses are required to provide visible image on a screen adjacent to the eye, bulky configuration and heavy weight are the common problems in the optical system of conventional head mounted displays, especially when the field of view is increased. FIG. 1 shows the schematic diagram of the optical system in such a prior art. According to U.S. Pat. No. 4,130,832 issued to Sher on Dec. 19, 1978, and U.S. Pat. No. 5,355,181 issued to Ashizaki et al on Oct. 11, 1994 and U.S. Publication No. 2004/0130783 A1 published on Jul. 8, 2004, inventions about 3-D head mounted displays using variable focal length elements to modulate scanning light beam provided a solution to relating visual accommodation with the stereoscopy.
However, the high cost, complex configuration, high requirements of components arrangement accuracy are significant problems. According to prior art publications include Ren, Hongwen, Tunable microlens arrays using polymer network liquid crystal, Optics Communication, vol. 230 (2004), p. 267-271, and Lin, Yi-Hsin et al., Tunable-focus cylindrical liquid crystal lenses, Japanese Journal of Applied Physics, vol. 44 (2005), p. 243, and Ren, Hongwen, Tunable-focus flat liquid crystal spherical lens, Applied Physics Letter, vol. 84 (2004), p. 4789, several tunable focus liquid crystal lens were described.
Therefore, a need exists for a low cost method and device of head mounted display providing stereoscopy images with visual accommodation and the presented device is slim and light weight.